Well, my Seagate Barracuda 500GB suffered a power failure. After that when I booted Windows it just got stuck at the blue starting screen and since then I can't boot anything off it.

I have Windows 7 & Gentoo Linux installed on it and I'm using GRUB to multiboot. The HDD is detected at POST and even GRUB loads off it.
Gentoo Linux loads but encounters a lot of I/O errors so gets stuck while booting.
On booting Win7, it waits a while and says that it can't find the partition and on booting Gentoo Linux after that, I get the same message. On rebooting, the hard disk doesn't get detected in POST either. It is again detected only when I unplug the power from the motherboard, plug it back in and then switch on.

From GRUB's CLI, I can see that all partitions are fine with files intact except for the partition on which windows resides which when I try to view, I get "nothing found". And after that, on trying to view other partitions results in the same message.
On booting into Win7 on another hard disk, the partitions of the hard disk in question aren't present.

I tried SeaTools, TestDisk and some other tools all of which encounter read errors while accessing any part of the hard disk.
These are the errors in the log

It seems a dead situation to me but I'm hoping that the data can somehow be salvaged. I don't care about the hard disk. I just care about the data.